Other Parts Discussed in Thread: BQ51013,
Tool/software:
Dear TI,
Problem: when charging using a 5.0V DC power source, the battery is fully charged successfully, but as it discharges, the recharge detection threshold never triggers.
Context: We are using the same circuit board for two different variants of the same product. One variant wirelessly charges via Qi WPT protocol, and the other variant wired-charges with a 5.0V DC power supply.
Circuit: I am using the two chips: BQ51013 and BQ25060 together to provide wireless and wired charging options for our battery-powered product. The BQ51013 creates a Qi wireless power transfer interface (selected when R41 is populated, and R42 is not), and accepts a wired DC charging input (selected when R42 is populated, and R41 is not). The BQ25060 chip directly interfaces with our battery pack (1S2P Li-ion, 5200mAh). Circuit diagram below. The BQ25060 is configured to deliver a 1.0A charging current to the battery, and the system draws power from the battery too (ie. there is not a separate power path for the rest of the system - the schematic net "VDD_BAT_IN".
Expected behaviour: With either wireless or wired charging variants, I would expect that the battery would become fully charged, and then for charging to stop. And if I leave the product on the wireless charging TX pad, or if I leave the product plugged into its 5.0V DC power source, I would expect to see the battery voltage to slowly decrease as the product draws its standby current from the battery. According to the BQ25060 datasheet, I would expect that recharging would be triggered according to the "V_RCH" recharge detection threshold, which can vary between –0.13V and –0.065V. I take this to mean that recharging would be triggered when the battery voltage falls to between 4.07–4.135V. So the end result would be the battery voltage rising and falling between 4.20V and 4.07V, as it charges, discharges and recharges again.
Observed behaviour: With wireless charging, everything behaves as described above. With wired charging, the recharging function never triggers - ie. the battery (starting at 0% SOC) charges up successfully for the first time, and then discharges (due to standby current draw from the rest of the circuit) until it is at 0% again. At a certain point, the system reaches such a low voltage that it shuts down, and then charging is triggered again.
Comment from our product testers: "You told me that the product would take 10 hours to fully recharge from 0% to 100%. I left it charging over the weekend, and the product tells me it is only at 20% battery!"
Question - please could you check our schematic, and comment on this behaviour, and see if there is anything we can change to get the desired recharge behaviour?
Thank you for your time.
Circuit schematic (power stage only):
Wireless charging battery voltage profile, clearly showing battery voltage rising and falling between 4.20V and 4.07V (blue trace. ignore the red trace) - i.e. correct behaviour:
Wired Charging battery voltage profile showing battery voltage rising to ~4.20V (100% SOC) and then falling down below the recharge detection threshold (should be min. 4.07V) - ie. incorrect behaviour:
